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Sounds like diatoms to me. They are very common in new set-ups or in tanks with new substrate. They are mostly caused by silicates being leached into the water from the substrate. Once the silicates are gone, so to will be the diatoms

They are harmless. Just clean them off and do a few extra water changes. They typically go away on their own in a few months

If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease."Not using a quarantine tank is like playing Russian roulette. Nobody wins the game, some people just get to play longer than others." - Anthony CalfoFishless CycleCycling with FishMarine Aquarium Info [URL="http://saltwater.aquaticcommunity.com/"]

I hope this is a typo - that your temp range isn't that extreme; do you mean 29-30 C?

Knowledge is fun(damental)

A 75 gal with eight Discus, fake plants, and a lot of wood also with sand substrate. Clean up crew is down to just two Sterba's Corys. Filters: continuous new water flow; canister w/UV, in-tank algae scrubber!! Finally, junked the nitrate removal unit from hell.